Keratoprosthesis may be used in children with bilateral corneal blindness

With comprehensive preop, intra-op and postop care, keratoprosthesis enables early and sustainable visual improvement.

Thomas John

Pediatric bilateral corneal blindness is a highly complex condition for a single surgeon to manage solo. A cornea specialist alone may not be able to provide complete visual care in such difficult cases.

Timely visual rehabilitation in these young children is of paramount importance to prevent lifelong amblyopia and dependence on family members and others in society. Corneal transplantation in these cases often results in only temporary visual rehabilitation and eventually corneal graft rejection, cloudy cornea and a return to corneal blindness. An alternative approach is to consider using the pediatric Boston keratoprosthesis, with the pediatric ophthalmologist as the central care coordinating physician while cornea, glaucoma and retina specialists form the outer circle of support in a multispecialty approach to provide optimal care for these children.

In this column, Drs. Aquavella and Ford describe their group’s experience with the use of pediatric Boston keratoprosthesis in their attempts to visually rehabilitate children with bilateral corneal blindness. A group approach with anterior and posterior segment specialists is used, and valuable technical pearls are covered.

— Thomas John, MD
OSN Surgical Maneuvers Editor

Congenital corneal opacity is, fortunately, a relatively rare occurrence. Our first infant keratoprosthesis implantation was performed in 2003. More than half of the 60+ eyes we have treated presented with a diagnosis of Peters anomaly, while other chromosome defects and congenital glaucoma account for 25% of our cases. Because the degree of related dysgenesis varies significantly, it is difficult to compare results with those of traditional corneal transplantation. Published studies of infant penetrating keratoplasty reveal different endpoints: graft clarity, incidence of allograft rejection and visual acuity. Other differences relate to primary or repeat grafts as well as refractive data.

While we firmly believe that keratoprosthesis is the procedure of choice for these infants, there are some who would prefer a single attempt at a corneal transplant and reserve the prosthesis for very vascularized cases or for after graft rejection. Our preference in bilateral cases is for primary keratoprosthesis surgery in the first eye as soon as feasible after 6 weeks of age and the second eye the subsequent week.

In the final analysis, the maximum level of ultimate and sustainable visual acuity is the desired goal. Thus, we must also consider the prospects for amblyopia prevention. The degree of discomfort, ocular surface inflammation, regular and irregular astigmatism, and anisometropia associated with traditional corneal transplantation must all be considered as impediments to the establishment of optimum visual acuity and delays in the process of amblyopia therapy. Graft clarity, corneal edema, surface irregularity and endothelial dysfunction are difficult to judge in infants who cannot be examined with a slit lamp.

This population presents numerous inherent difficulties. Not only are these eyes small, but they are prone to a variety of inflammatory events regardless of the type of surgical intervention. Thirty percent of our cases present with or subsequently develop vitreoretinal pathology. Glaucoma is always a threat. About 15% of eyes either present with shunts or require them subsequently. Cardiac, pulmonary, digestive and cranial facial pathologies are often present.

Preoperative appearance of Peters anomaly in a 4-year-old with four previous grafts.

Postoperative appearance. Now 6 years old, the patient has uncorrected reading vision postoperatively. Images: John T, Aquavella JV, Ford RM

Preoperative Peters anomaly with significant dysgenesis.

Postoperative appearance.

Postoperative keratoprosthesis with shunt that was placed following keratoprosthesis implantation.

Three-year postoperative appearance. Semi-scleral bandage lens in place over prosthesis. Patient wears goggles to maintain ocular surface.

Device and procedure

The clear plastic surface of the prosthesis precludes anisometropia and astigmatism and ensures excellent optics and maximum potential acuity from the first few postoperative days. These optics remain in place without degradation or potential reduction due to allograft rejection. Thus, one of the major benefits of keratoprosthesis is the prospect for early and sustainable visual improvement. However, these benefits can only be achieved in the presence of comprehensive preoperative, intraoperative and ongoing postoperative care. The responsibility for assembling the individuals who will provide the care resides with the initial operating team and the family. A team approach involving cornea, vitreoretinal, pediatric and glaucoma subspecialists is mandatory. Follow-up care must be arranged and put in place before surgery. This may be difficult because some portions of care will be provided by the operative team, while monitoring and subsequent intervention may be in the hands of ophthalmologists who reside near the patient.

The natural lens must always be removed, so surgeons need to rely upon the axial length measurement to order the appropriately powered aphakic Boston type 1 keratoprosthesis. Usually a few diopters of planned hyperopia may be selected in anticipation of subsequent myopic growth. While back plates in a smaller 7.25-mm diameter are available, we have found that the standard 8.5-mm diameter back plate is preferable for most infant eyes. Indeed, there is some evidence that the larger-diameter back plates may reduce retroprosthetic membrane formation. Newer titanium back plates will soon be available. The cosmetics with these fenestrated plates are not as desirable as those evidenced with the standard methyl methacrylate material, but there is some evidence that the titanium is better tolerated by the ocular tissues.

Pars plana vitrectomy must be a part of the original surgery. This can be performed by preliminary implantation of a temporary keratoprosthesis, enabling facile visualization for subsequent pars plana vitrectomy, and then replacement with the permanent keratoprosthesis. Experienced pediatric vitreoretinal surgeons soon become comfortable working through the 3.25-mm optic of the prosthesis, enabling omission of this step. Subsequent growth in axial length and related refractive changes may be compensated for by changing the power of the overlying bandage lens. In infants, the presence of a bandage lens over the prosthesis is extremely important and must be encouraged even at the expense of placing a partial tarsorrhaphy.

Technical pearls

1. The infant is paralyzed by anesthesia before the eye is entered.
2. A peritomy is advisable to enable more accurate centration and diameter selection.
3. A Flieringa fixation ring is helpful.
4. Preparation of the donor tissue and device should precede removal of the pathological cornea so that they can be placed rapidly.
5. Donor endothelial cell viability need not be considered.
6. We prefer an 8.75-mm donor diameter placed in a recipient bed of 8.25-mm diameter.
7. Partial-depth trephination followed by needle cautery will minimize bleeding into the anterior chamber and speed the process of obtaining optimal acuity.
8. Vascularized iris adhesions require careful guarded excision of the cornea.
9. If the iris is intact, a peripheral iridectomy is mandatory.
10. Lensectomy is needed in all cases. We prefer to use an aphakic keratoprosthesis and avoid IOLs.
11. Prepare the angle by passing a spatula and injecting viscoelastic.
12. The implant is sutured with eight to 12 sutures of 9-0 or 10-0 nylon.
13. Always place a hydrophilic bandage lens. A 16-mm lens is provided with the keratoprosthesis.
14. A light patch with antibiotic drops is placed for 24 hours.
15. We administer a Tylenol (McNeil) suppository at surgical conclusion, but no systemic pain medications are necessary.
16. Office exams should occur in 24 and 72 hours postop, then weekly for 3 weeks. Examinations under anesthesia including axial length and B-scans as well as IOP estimation are needed every 3 months for 1 year.
17. Topical anti-inflammatory steroid should be used four times a day for the first year and in the absence of retroprosthetic membrane can be slowly tapered.
18. A bandage lens for these infants is essential for the first year and must be maintained. Moist chamber goggles may assist in the lens wear.

Standard postoperative orders

No pain medication is necessary. Vancomycin 14 mg/mL and a fluoroquinolone twice a day for 1 month, then daily indefinitely, should be given along with 1% methyl prednisolone four times a day, only tapered after several months with no evidence of retroprosthetic membrane. The bandage lens must be refitted if necessary and maintained. Anti-evaporative goggles may assist in maintaining hydration of the bandage lens.

References:

• Aquavella JV. Pediatric keratoprosthesis: a new surgical approach. Ann Ophthalmol (Skokie). 2008;40(2):64-67.
• Aquavella JV, Gearinger MD, Akpek EK, McCormick GJ. Pediatric keratoprosthesis. Ophthalmology. 2007;114(5):989-994.
• Colby KA, Koo EB. Expanding indications for the Boston keratoprosthesis. Curr Opin Ophthalmol. 2011;22(4):267-273.
• Greiner MA, Li JY, Mannis MJ. Longer-term vision outcomes and complications with the Boston type 1 keratoprosthesis at the University of California, Davis. Ophthalmology. 2011;118(8):1543-1550.

• Thomas John, MD, is a clinical associate professor at Loyola University at Chicago and is in private practice in Oak Brook, Tinley Park and Oak Lawn, Ill. He can be reached at 708-429-2223; fax: 708-429-2226; email: tjcornea@gmail.com.
• James V. Aquavella, MD, and R. Marshall Ford, MD, can be reached at the Department of Ophthalmology, University of Rochester Flaum Eye Institute, 601 Elmwood Ave., Box 659, Rochester, NY 14642; email: james_aquavella@urmc.rochester.edu.
• Disclosure: Drs. Aquavella, Ford and John have no relevant financial disclosures.